The present invention relates to a dry mix cement composition. More particularly, the invention relates to a dry mix cement composition that includes an alkaline glassy aluminosilicate material. Generally the alkaline glassy aluminosilicate material is included as a polymerisation aid in a cement composition including other aluminosilicate materials such as fly ash or blast furnace slag. However, it should be noted that in some instances the alkaline glassy aluminosilicate material will be included as the sole component in the composition.
Cements may generally be divided into two groups, those being hydraulic cements and geopolymeric cements. Hardening of conventional hydraulic cements is the result of hydration of calcium aluminates and calcium silicates within the cement composition. In opposition to this, geopolymeric cements result from mineral polycondensation reactions achieved by alkaline activation. This process is sometimes coined as geosynthesis.
In the art of geosynthesis, the term “poly(sialate)” has been adopted to refer to aluminosilicate geopolymers. The sialate network consists of SiO4 and AlO4 tetrahedrons alternatively bound by oxygen atoms. Cations (Na+, K+, Ca++, H3O+) present in the structural cavities of the poly(sialate) balance the negative charge of Al3+ in coordination (IV).
The empirical formula of polysialates is:Mn{—(SiO2)z-AlO2}n,wH2Owith M representing the cation K, Na or Ca; n the degree of polymerization; and z being equal to from 1 to 32.
The three-dimensional network (3D) geopolymers are of type:poly(sialate)M-PS Si:Al=1:1Mn—(—Si—O—Al—O—)n;  (i)poly(sialate-siloxo)M-PSS Si:Al=2:1 Mn—(Si—O—Al—O—Si—O—)n;  (ii)poly(sialate-disiloxo)M-PSDS Si:Al=3:1Mn—(Si—O—Al—O—Si—O—Si—O—)n.  (iii)
The geopolymeric binders or cements of the types poly(sialate), poly(sialate-siloxo) and poly(sialate-disiloxo), have been the subject of several patents in which their particular properties have been highlighted. One can quote for example the French patents: FR 2.489.290, 2.489.291, 2.528.818, 2.621.260, 2.659.319, 2.669.918, and 2.758.323. Geopolymeric cements of the prior art, for example International Publication Nos. WO92/04298, WO92/04299, WO95/13995, and WO98/31644, are the result of a polycondensation reaction between three distinct mineral reagents:
a) aluminosilicate oxide (Si2O5, Al2O2);
b) potassium or sodium disilicate (Na, K)2(H3SiO4)2; and
c) calcium disilicate Ca(H3SiO4)2 
With potassium disilicate, polycondensation is the result of the following chemical reaction:2(Si2O5,Al2O2)+(Na,K)2(H3SiO4)2+Ca(H3SiO4)2→(K2O,CaO)(8SiO2,2Al2O3,nH2O)  (1)
The geopolymer obtained is of the type (K, Ca)-Poly(sialate-siloxo), (K, Ca)—PSS, with Si:Al=2. Various reactive mineral fillers, such as silica (silica fume), or natural aluminosilicates may be added to the geopolymer.
The reagents a) and b) are industrial reactive products included in the reactive medium. Conversely, ingredient c), calcium disilicate, occurs in a naissant state, in situ, in the strong alkaline medium. Generally, this is a result of a chemical reaction involving calcium silicate, such as calcium mellilite, present in blast furnace slag.
Conventionally, geopolymers are synthesised by using a two part mix including an alkaline soluble silicate solution and a solid mixture of aluminosilicate materials. For instance, a manufacturing process for a geopolymer of the type (Na, K)-poly(sialate-disiloxo), (Na, K)—PSDS, is described in European Patent No. EP 0 518 980. This process exclusively uses an alkaline solution of a very special silica obtained in an electric furnace and the reactive mixture contains sodium or potassium alkaline silicates, but does not include any calcium Ca.
In International Publication No. WO92/04299 a cement containing tecto-alumino-silicates resulting from the reaction between metakaolin, reactive silica, aluminosilicate chemically activated at a temperature between 800° C. and 1200° C., soluble alkali silicate, alkali hydroxide (KOH or NaOH), and calcium silicate is described. The aluminosilicate cement has an atomic ratio Al:Si in the range of 4:6 to 4:14, that is to say a Si:Al ratio varying from 1.5 to 3.5.
More recently, United States Patent Application No. 20050172860 describes a cement binder that contains type (K,Ca)-Poly(sialate-disiloxo), (K,Ca)—PSDS, geopolymer resulting from the reaction between a residual rock from a strongly weathered granitic type, calcium mellilite glass, and a soluble alkaline silicate in which the molar ratio (Na, K)2O:SiO2 ranges between 0.5 and 0.8.
There are many drawbacks associated with traditional two part mixes for the synthesis of geopolymers. The caustic alkaline solutions needed to form the geoploymers make the handling and application of the geopolymers difficult. Also, workability is generally poor and not easily adjustable due to a sticky and thick mortar that is generated during processing. The system is also sensitive to the ratio of alkaline and soluble silicate, which is difficult to control in practice. Still further, the routine practices used in cement industries, such as the construction industry, can not be applied using geopolymeric cements due to their totally different characteristics in terms of rheology, chemistry and workability.
Most importantly, the alkaline and/or soluble silicates that are added during processing cannot be totally consumed during geopolymerisation, even with curing at a raised temperature, due to the existence of dissolution equilibrium of raw aluminosilicate materials in alkaline silicate solutions. This causes severe efflorescence of the final geopolymer products and high permeability and water adsorption due to the movement of alkali together with water to the geopolymer surfaces.
The present invention provides an alternative to the conventional two part mixes and advantageously alleviates one or more of the disadvantages of the prior art.
While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.